Mick Mulvaney on Tuesday said he would defy a U.S. congressional subpoena seeking his testimony as part of the impeachment inquiry, abruptly dropping plans to file a lawsuit to confront whether House Democrats could force him to sit for questioning.

The about-face came a day after Mulvaney's lawyer, William Pittard of Washington's KaiserDillon, told a Washington federal trial judge that the acting White House chief of staff would file his own suit confronting the power of House Democrats to compel top Trump officials to testify.

Mulvaney had previously pressed to join a lawsuit filed by former National Security Adviser John Bolton's deputy, Charles Kupperman, who went to court seeking clarity on whether he could comply with a congressional subpoena or follow the White House's instructions to not cooperate with the impeachment inquiry.

"After further consideration, Mr. Mulvaney does not intend to pursue litigation regarding the deposition subpoena issued to him by the U.S. House of Representatives," Pittard said in a court filing Tuesday. "Rather, he will rely on the direction of the President, as supported by an opinion of the Office of Legal Counsel of the U.S. Department of Justice, in not appearing for the relevant deposition."

During a telephone conference on Monday, the judge overseeing Kupperman's case expressed reluctance to allow Mulvaney to join Kupperman's lawsuit. Kupperman's lawyer, Charles Cooper of Cooper & Kirk in Washington, resisted Mulvaney's bid to join the lawsuit, saying the acting White House chief of staff had "made it clear in his papers and in public statements by his counsel that he's entirely aligned with the president."

Kupperman, on the other hand, "takes no position on the merits of the issue," Cooper said in the Monday evening telephone conference, according to a transcript of the call.

"He is, and will remain, neutral throughout these proceedings," Cooper said. "So not only will we not adequately represent the interests of Mr. Mulvaney, we won't represent them at all."

Charles Cooper Charles Cooper, of Cooper & Kirk, and Attorney General Jeff Sessions's attorney, during Sessions's testimony before the Senate Intelligence Committee, on June 13, 2017.

U.S. District Judge Richard Leon said on the call that he was "not inclined" to grant Mulvaney's request to join Kupperman's case as an intervenor. Leon scheduled a hearing for Tuesday afternoon to address whether Kupperman would object to letting Mulvaney's would-be lawsuit be considered a "related" case. With that designation, Mulvaney's case would be handed directly to Leon, bypassing the court's random assignment process.

In his court filing Tuesday, Pittard said "Mulvaney respectfully suggests that there no longer is a need" for that hearing. Leon, noting Mulvaney's plans, scrapped the hearing.

The Washington Post reported Monday that Mulvaney's efforts to join Kupperman's suit "baffled several administration officials." The White House reportedly had insisted that Mulvaney's litigation plans were not adverse to the interests of the president. Still, the Post report described internal discord at the White House, with Mulvaney and Pat Cipollone, the White House counsel, at times at odds with each other.

House investigators are looking at how and why President Donald Trump tried to pressure Ukrainian officials to investigate Trump's political rivals, including Joe Biden, a leading Democratic contender in the 2020 presidential race. Trump has denied that he engaged in improper conduct, describing as "perfect" a closely scrutinized call in which he appeared to pressure his Ukrainian counterpart to mount an investigation into a domestic political rival.

Mulvaney last month appeared to acknowledge an explicit quid pro quo, but he later walked back those remarks, which were televised. Mulvaney's press statement, according to the Post and other media outlets, complicated the White House positioning that Trump had not used the power of the presidency to urge a foreign power to meddle in U.S. elections.